Websocket not sending text?

I have a small "server" applet in Python that launches an application and starts a server waiting for some data via websocket:

#!python3
import os
import subprocess

import asyncio
import websockets

async def hello(websocket, path):
    name = await websocket.recv()
    print("< {}".format(name))

    greeting = "Hello {}!".format(name)
    await websocket.send(greeting)
    print("> {}".format(greeting))

subprocess.Popen(['C:\\...\\some_app.exe', 'd:\\data\\app_data.txt'])

start_server = websockets.serve(hello, 'localhost', 8765)
asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()

The application has a plugin that uses Javascript websockets to connect to the server. In the global part of the js file, I establish a connection:

const socket = new WebSocket('ws://localhost:8765');

//
socket.addEventListener('open', function (event) {
    socket.send('Connection Established'); 
});

socket.addEventListener('message', function (event) {
    console.log(event.data);
});

The connection does get established when this code runs, however, in another function, when I try to send data, it fails:

alert("Gonna use socket!");
if (socket.readyState == 1) {
    socket.send('foo'); 
    socket.close();
} else {
    alert("Socket not ready!");
}

Why does the socket get closed? Is there any way to keep it open (or is that bad practice)?